Almost all valves consist of a fixed body containing a hole or port covered by a sealing element. This sealing element (valve) can uncover the port to varying degrees and allow fluid to flow. The arrangement of these elements generally takes the form of axial pairs (lift valve), turning pairs (rotary valve motion), screw pairs (helical valve motion), and sliding pairs (gate valve). These valve elements are accepted practice, have been utilized for centuries and there are many manufacturers using these principles to accomplish the same task.
The miniature valve market, typified by manufacturers like Clippard, Pneumadyne and Whitey, offer a variety of metering valves. However, all are needle valve designs. Needle valves are capable of precise metering but have several drawbacks. A needle valve is an axially arranged device and its accommodation to applications usually require shapes, ports and manufacturing complexity. In order to adjust flow rates a tapered needle is screwed in and out of a circular aperture enabled by threads coaxially constructed along the needle shaft. The resulting space offered as a flow passage is at best an annulus (and often deteriorates to a crescent) where the area varies with axial needle position created by screw threads. Area is an arithmetic function of the radii squared and accordingly the range of linear sensitive control is only approximate and at the same time narrow. Also, unless the same material is used throughout, the valve differential expansion leads to an inherent lack of temperature compensation. Furthermore, the tiny clearances generated clog easily and good filtration of the medium is required. Unless exceptionally complex shapes, and/or threads and/or controls are used in the design of the valve, the flow through needle valves is not a linear function of needle position. The needles themselves require precision manufacturing techniques. Since the needle requires several rotations from off to fully open they do not lend themselves to rapid automatic operation. It is also very difficult to arrange a needle valve for “fail safe” operation, i.e., should the valve actuator loose power, the valve cannot be spring or gravity returned to the off position. Moreover, the needle and seat surfaces are subject to damage due to brinelling scuffing and scoring.
Accordingly, there is a need for a valve that solves the problems associated with needle, ball and butterfly, valves. It is among the objects of the invention to provide a valve that simplifies manufacturing requirements. Another object of the invention is to provide a valve the provides a linear response curve. A further object is to provide a valve that allows for customized flow resistance versus valve position. These and other objects will become apparent from a reading of the following summary and detailed description of the illustrative embodiment.